This invention relates, in general to a hydrocarbon/hydrogen based selective process, and more particularly, to selective etching of III-V semiconductor materials or the selective deposition of hydrogenated carbon materials.
One of the key steps in manufacturing gallium arsenide field effect transistors is the removal of a gallium arsenide (GaAs) n.sup.+ contact layer overlying an aluminum gallium arsenide layer. (AlGaAs) without etching of the AlGaAs layer. In the past, a complicated, pH controlled, wet chemical etch or dry etching has been utilized. Wet chemical etching results in nonuniformities across a substrate, therefore, some over-etching was required to ensure the complete removal of the gallium arsenide layer across the entire substrate.
A disadvantage of this wet process was that the pH of this wet chemical etchant had to be monitored extremely carefully during the entire etch process in order to maintain high selectivity between the GaAs layer and the AlGaAs layer. Another disadvantage was that the over-etch process undercut the gallium arsenide layer and thus degraded device performance and caused nonuniformity of device characteristics across the substrate.
Selective dry etching has been demonstrated using chlorine/fluorine based chemistries. However, all of these processes involve gases that are corrosive, toxic and environmentally hazardous.
In order to fabricate devices having superior and uniform electrical characteristics, it is desirable to minimize the undercut length of the GaAs layer and to minimize nonuniformities in the etch of the GaAs layer.